Quenching process utilizing compressed air

ABSTRACT

A method for quenching a metal workpiece having an internal passage with at least one open end, wherein the workpiece has a plurality of bore holes extending between the internal passage and the external surface, the method including the steps of pressurizing the internal passage with a pressurized fluid source to prevent quenchant from entering the internal passage and the plurality of bore holes; flowing quenchant across the external surface to cool and harden the workpiece.

TECHNICAL FIELD

A method generally related to heat treatment processes, and morespecifically to an improved method for the heat treatment of metal partshaving internal passages, utilizing compressed air to prevent quenchantfrom entering the internal passages of the heat-treated part.

BACKGROUND

It is common practice, for example in the metallurgical art, to heattreat and then cool or quench a workpiece or part for one or more of avariety of reasons. This heat treatment and cooling process may be usedto develop desired microstructure and mechanical properties in the metalpart, with the typical desire to avoid physical defects such ascracking, distortion and residual stresses which impact suchcharacteristics as machinability during manufacture, assembly, orrepair, and fatigue life of the part.

Within the context of this disclosure, heat treatment should beunderstood to mean any technique for the treatment of a ferrous (iron)substrate material such as steel, or any other metal part which involvescooling at least part of the said substrate material, especially,tempering, nitriding, carburizing, surface coating, plasma spraying,oxycutting, laser cutting, HVOF (high-velocity oxyfuel) spraying, flamespraying, etc. These various heat-treatment techniques are known andwidely used in the industrial field.

Often the heat-treated metal parts are elongated and have one or moreinternal passages such as a shaft, cylinder tube, or the like, formaterial or fluid flow. The internal passages may run the full length orwidth of the part or not, and, they may intersect or cross one another.

A variety of methods and apparatuses for cooling certain parts andworkpieces have been reported. It should be appreciated that the coolingor quenching treatment utilized in the present disclosure can be anytreatment that serves to increase the hardness of the treated metal of awork piece with an internal passage.

Quenching of a workpiece with internal passages renders several issuesthat can lead to poor workpiece quality, increased waste and enormousproduction costs. Because the quenchant is allowed to contact both theinternal passages and the external surface, rapid cooling occurs. Theinternal passages allow quenchant to flow through and between thesepassages, which causes rapid cooling as the quenchant is in directcontact with the internal passages and external surface. The rapidcooling can cause a build up of stress cracks in the workpiece.

The internal passages (which may also include cross holes, boreholes oroil holes or other secondary external surface passages, of varyingdiameter) can also harden out during quenching. Further, on a workpiecewith more than one internal passage where the passages intersect eachother, the likelihood of the aforementioned issue is elevated. Yetfurther, where the internal passages on the workpiece intersect and meetat a 90-degree angle, stress concentrators have been found at theintersection of those internal passages where quenchant remainsfollowing the quenching process, leading to an ever-increasedconcentration of stress, and ultimately stress cracking.

In the case of a workpiece with internal passages intersecting, the areaof highest stress would be at the point creating a sharp angle (i.e., 90degrees). This area of high stress build up is where cracks may formduring and following quenching. Normally, either a radius or a chamferwould be used on an external surface to prevent the creation of a stressconcentrator. However, due to the internal location of the intersectingpassages, it is not feasible to create a chamfer or a radius in order todecrease the build up of quenchant, and therefore metallurgical stress,that can be developed at the intersection.

In the present disclosure, stress build up caused by fast quenching andquenchant remaining in the internal passages and boreholes wasprevented. This was achieved by advancing compressed gas through one endof the workpiece and out through the cross or bore holes. By keepingquenchant out of the internal passage and boreholes, it allowed theinternal passages of the workpiece to cool at a much slower rate. Theslower cooling rate keeps stress from building up generally, especiallyin this area of concern, and the cracks that were forming upon quenchingare prevented.

In the past, in order to overcome this problem of stress build up and tobetter control the cooling rate of the internal passages in theworkpieces, operators attempted to prevent quenchant from entering thepassages and boreholes, by utilizing appropriately sized bolts manuallyplaced in the boreholes. Additionally, steel wool has been used to plugor fill the holes and passages.

These previously known passage-plugging techniques present severalproblems, including steel wool fusing to the part and being difficult toremove, or actually preventing proper hardening of the external surfacedue to the density of the plug material or the contact of the manuallyplaced bolt heads to the external surface.

Further, in a patent to White et al. (U.S. Pat. No. 6,216,710) a methodof removing liquid from pores contained in a permeable metal part isdisclosed. A cleaning fluid is injected into the interior chamber of thepart, and then the interior chamber is pressurized using a compressedgas causing the cleaning fluid to permeate through the pores to theexterior surface. The White et al. patent also teaches removing residualquench oil from a powered metal product after it has been quenched.However, the prior art process does not affect the quench rate at alland is not even used in the traditional heat treatment related quenchingprocess. Also, it is only applicable to porous material such as a powdermetal product.

The present disclosure is directed to overcoming one or more of theproblems set forth above.

SUMMARY

The present disclosure, in one form, provides a method for quenching ametal workpiece having an internal passage with at least one open end.The workpiece has a plurality of boreholes extending between theinternal passage and an external surface. The method includes the stepsof pressurizing the internal passage with a pressurized fluid source toprevent quenchant from entering the internal passage and the pluralityof boreholes and flowing quenchant across the external surface to cooland harden the workpiece.

Other advantages and novel features of the present disclosure willbecome apparent from the following detailed description of thedisclosure when considered in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of an exemplary workpiece for use in thepresent disclosure.

FIG. 2 is an illustrative side view of an embodiment of the presentdisclosure.

FIG. 3 is an enlarged partial cross sectional view, partial schematicview of an embodiment of the present disclosure.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for the purposeof illustrating the preferred embodiments of the disclosure only, andnot for the purpose of limiting the same, FIG. 1 illustrates a metalworkpiece 10 having an internal passage 12 and a plurality of boreholes14. The workpiece 10 has at least one open end 18. The boreholes 14 aresecondary internal passages that may run perpendicular to the directionof the internal passage 12, thereby creating an intersection 16, wherethe internal passage 12 and the boreholes 14 meet. The intersection maybe at a 90-degree angle, and the diameters of the internal passage 12and the boreholes 14 may be different. The workpiece 10 may be of anelongated shape, and made from a ferrous material or the like. Theworkpiece 10 is heat treated prior to the quenching process. The heattreatment, as would be known by those skilled in the art, may be of anymeans including but not limited to carburizing or hardening, conductedby furnace heating, induction heating, casting or forging.

FIG. 2 is useful in explaining the construction and operation of thequenching station 30. A mechanical mechanism (not shown) such as aconveyor or pulley system, or the like, operates to move the workpiece10 from a heat treatment area to the quenching station 30.

In accordance with one embodiment of the present disclosure, theworkpiece 10 is lowered into or immediately above a quench trough 40.The workpiece 10 may be supported and contained at selected positions bya plurality of locators 42 within or on (as seen in FIG. 3) the quenchtrough 40. The locators 42 may also provide opposed restraint againsttransverse deflection (not shown). The quench trough 40 is sufficientlysized to collect the volume of quenching liquid or quenchant 60 neededto cool each workpiece 10 or batch of workpieces, as may be seen in alarge production facility. While the aforementioned quenching process isdiscussed as completed via batch style processing, it will beappreciated that the method may be appropriately arranged for continuousprocessing.

A storage tank 50, independent of quench trough 40, and having aquenchant containing bottom 52 and sides 54 is arranged vertically aboveand immediately adjacent to or over the quench trough 40. The quenchant60 is contained within storage tank 50. The storage tank 50 may have apipe 64 and be optionally provided with a valve 66, extending from oneof the sides 54 adjacent the bottom 52 thereof, immediately over thequench trough 40. Storage tank 50 may have an inlet opening 62 which maybe connected, by means of a pipe 65 having a pump 68 integral therein,to an outlet 70 of the quench trough 40. The pump 68 is operable to drawquenchant 60 out of the trough 40. Optionally, the quenchant 60 may becooled through a heat exchanger for example (not shown) after being usedfor quenching, as the quenchant 60 may absorb heat from the workpiece10.

As seen in FIG. 2 and FIG. 3, with the workpiece 10 contained andsupported within the quench trough 40, at least one adapter 22 may beconnected to at least one open end 18 of the workpiece 10. At least oneadapter 22 may then be coupled 24 into fluid communication with apressurized fluid source 26 via conduit 24. The pressurized fluid sourcemay optionally be any compressed gas suitable for cooling a metalworkpiece 10.

The pressurized fluid source 26 may be pneumatically operated (notshown). As would be known, the source may include a compressor toadvance the compressed gas to a pneumatic line, and a pneumatic valvefor activation and deactivation. When activated, the source 26 advancesthe pressurized fluid 26 through the adapter 22, into the internalpassage 12 of the workpiece 10. The pressurized fluid 26 exits throughthe plurality of bore holes 14.

After pressurized fluid is advancing through workpiece 10, valve 66 isopened allowing quenchant 60 to rapidly flow over the workpiece 10. Itwould be understood that the quenchant 60 may be directed upward intothe quench trough 40 to immerse the workpiece (as shown in phantomlines), or optionally, quenching station 30 may be arranged as animmersion station, where the workpiece 10 is submersed (not shown) inthe quench trough 40 for an appropriate time for cooling. Thepressurized fluid source 26 operates to advance compressed gas throughthe internal passage 12 and out of the boreholes 14 at a pressuresufficient to prevent quenchant 60 from entering the inner cavities ofthe workpiece 10.

By advancing the compressed gas 26 through at least one end of theworkpiece 10 and out through the boreholes 14 at the sufficient rate,the quenchant is kept out, allowing the internal passages 12 and 14 ofthe workpiece to cool at a much slower rate. The slower cooling ratekeeps stress from building up generally, especially in the special areasof concern 16, thereby preventing stress cracks in the workpiece.

It will be appreciated by those skilled in the art that given the flowrate of the quenchant, and the dwell time, that is the time for whichthe workpieces are exposed to the quenchant 60, is a function of thesize, shape and length of the workpiece 10.

INDUSTRIAL APPLICABILITY

The industrial applicability of the quenching method described hereinwill be readily appreciated from the foregoing discussion. A method isdescribed wherein quenching results in a cooled and hardened workpiece10 with an internal passage 12 and plurality of boreholes 14 free fromquenchant 60. Therefore the internal passage 12 and boreholes 14 are notsusceptible to stress concentrators (not shown) building up at theinternal intersections 16. Furthermore, preventing quenchant fromentering the passage and boreholes allows the workpiece 10 to cool at aslower rate. It should be understood that a slower cooling a workpiece10 with an internal passage further decreases the opportunity for thebuild up of stress concentrators.

Examples of the present disclosure are applicable to any quenchingsystem employing a workpiece with an internal passage where it isdesired that the internal passages of the workpiece are kept free fromquenchant. For example, many elongated workpieces, such as input shafts,have a plurality of boreholes that intersect the internal passages andform internal 90 degree angles, may benefit from application of theteachings herein. In such workpieces, application of the foregoingmethod can provide better quality components and machine parts, freefrom stress and cracks, etc.

It will be appreciated that the foregoing description provides examplesof the disclosed method. However, it is contemplated that otherimplementations of the disclosure may differ in detail from theforegoing examples. All references to the disclosure or examples thereofare intended to reference the particular example being discussed at thatpoint and are not intended to imply any limitation as to the scope ofthe disclosure more generally. All language of distinction anddisparagement with respect to certain features is intended to indicate alack of preference for those features, but not to exclude such from thescope of the disclosure entirely, unless otherwise indicated.

Recitation of ranges of values herein are merely intended to serve as ashorthand method of referring individually to each separate valuefalling within the range, unless otherwise indicated herein, and eachseparate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context.

Accordingly, this disclosure includes all modifications and equivalentsof subject matter recited in the claims appended hereto as permitted byapplicable law. Moreover, any combination of the above-describedelements in all possible variations thereof is encompassed by thedisclosure unless otherwise indicated herein or otherwise clearlycontradicted by context.

1. A method for quenching a metal workpiece having an internal passagewith at least one open end, wherein said workpiece has a plurality ofbore holes extending between said internal passage and an externalsurface, the method comprising the steps of: pressurizing said internalpassage with a pressurized fluid source to prevent quenchant fromentering said internal passage and said plurality of bore holes; andflowing quenchant across said external surface to cool and harden saidworkpiece.
 2. The method, as set forth in claim 1, wherein saidplurality of bore holes extending between said internal passage and saidexternal surface intersect said internal passage at near or equal to90-degree angles.
 3. The method, as set forth in claim 1, furthercomprising the steps of: connecting at least one adapter to said atleast one open end of said workpiece; coupling said at least one adapterinto fluid communication with said pressurized fluid source; anddirecting said pressurized fluid directly through said adapter into saidinternal passage of the workpiece, wherein said pressurized fluid exitsthrough the said plurality of bore holes.
 4. The method, as set forth inclaim 1, wherein said pressurized fluid source is compressed air at apressure greater than the flow pressure of said quenchant.
 5. Themethod, as set forth in claim 1, wherein the flowing step is performedby pouring quenchant across said external surface of said workpiece 6.The method, as set forth in claim 1, wherein the flowing step isperformed by submersing said workpiece in a quench bath.
 7. The method,as set forth in claim 1, wherein the flowing step is performed byspraying quenchant across said external surface of said workpiece. 8.The method, as set forth in claim 1, wherein the quenchant is a waterand polymer mix.